Activation of zeolites

ABSTRACT

A method for enhancing the activity of a crystalline zeolite, including a zeolite having a silica-to-alumina ratio greater than 100, is disclosed which involves impregnating the zeolite with an ammoniacal aluminum fluoride solution, contacting the impregnated zeolite with a warm aqeuous solution of an ammonium salt and then calcining the final product.

CROSS-REFERENCE TO RELATED CASES

This application is related by subject to the copending applicationsidentified as follows:

    ______________________________________                                        Serial Number                                                                           Filing Date                                                                              Serial Number                                                                              Filing Date                                 ______________________________________                                        319,175   November 9,                                                                              333,370      December 22,                                          1981                    1981                                        355,419   Herewith   355,418      Herewith                                    355,417   Herewith   355,416      Herewith                                    355,414   Herewith   355,413      Herewith                                    355,446   Herewith   355,420      Herewith                                    ______________________________________                                    

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for enhancing the acid activity of aporous crystalline aluminosilicate zeolite, including highsilica-containing porous crystalline zeolite materials, which involvesthe steps of impregnating the crystalline material with an ammoniacalaluminum fluoride solution, contacting the impregnated material withwarm aqueous solution of an ammonium salt, and calcining the ammoniumsalt solution contacted material. The resulting zeolite compositionexhibits enhanced Bronsted acidity.

2. Description of Prior Art

Zeolitic materials, both natural and synthetic, have been demonstratedin the past to have catalytic properties for various types ofhydrocarbon conversions. Certain zeolitic materials are ordered, porouscrystalline aluminosilicates having a definite crystalline structurewithin which there are a large number of smaller cavities which may beinterconnected by a number of still smaller channels. Since thedimensions of these pores are such as to accept for adsorption moleculesof certain dimensions while rejection those of larger dimensions, thesematerials have come to be known as "molecular sieves" and are utilizedin a variety of ways to take advantage of these properties.

Such molecular sieves, both natural and synthetic, include a widevariety of positive ion-containing crystalline aluminosilicates. Thesealuminosilicates can be described as a rigid three-dimensional frameworkSiO₄ and AlO₄ in which the tetrahedra are cross-linked by the sharing ofoxygen atoms whereby the ratio of the total aluminum and silicon atomsto oxygen is 1:2. The electrovalence of the tetrahedra containingaluminum is balanced by the inclusion in the crystal of a cation, forexample, an alkali metal or an alkaline earth metal cation. This can beexpressed wherein the ratio of aluminum to the number of variouscations, such as Ca/2, Sr/2, Na, K or Li is equal to unity. One type ofcation may be exchanged either entirely or partially by another type ofcation utilizing ion exchange techniques in a conventional manner. Bymeans of such cation exchange, it has been possible to vary theproperties of a given aluminosilicate by suitable selection of thecation. The spaces between the tetrahedra are occupied by molecules ofwater prior to dehydration.

Prior art techniques have resulted in the formation of a great varietyof synthetic aluminosilicates. These aluminosilicates have come to bedesignated convenient symbols, as illustrated by zeolite ZSM-5 (U.S.Pat. No. 3,702,886).

High silica-containing zeolites are well known in the art and it isgenerally accepted that the ion exchange capacity of the crystallinezeolite is directly dependent on its aluminum content. Thus, forexample, the more aluminum there is in a crystalline structure, the morecations are required to balance the electronegativity thereof, and whensuch cations are of the acidic type such as hydrogen, they imparttremendous catalytic activity to the crystalline material. On the otherhand, high silica-containing zeolites having little or substantially noaluminum, have many important properties and characteristics and a highdegree of structural stability such that they have become candidates foruse in various processes including catalytic processes. Materials ofthis type are known in the art and include high silica-containingaluminosilicates such as ZSM-5, ZSM-11 (U.S. Pat. No. 3,709,979), andZSM-12 (U.S. Pat. No. 3,832,449) to mention a few.

The silica-to-alumina ratio of a given zeolite is often variable; forexample, zeolite X (U.S. Pat. No. 2,882,244) can be synthesized with asilica-to-alumina ratio of from 2 to 3; zeolite Y (U.S. Pat. No.3,l30,007) from 3 to about 6. In some zeolites, the upper limit ofsilica-to-alumina ratio is virtually unbounded. Zeolite ZSM-5 is onesuch material wherein the silica-to-alumina ratio is at least 5. U.S.Pat. No. 3,941,871 discloses a crystalline metal organo silicateessentially free of aluminum and exhibiting an x-ray diffraction patterncharacteristic of ZSM-5 type aluminosilicate. U.S. Pat. Nos. 4,061,724;4,073,865 and 4,104,294 describe microporous crystalline silicas ororgano silicates wherein the aluminum content present is at impuritylevels.

Because of the extremely low aluminum content of these highsilica-containing zeolites, their ion exchange capacity is not as greatas materials with a higher aluminum content. Therefore, when thesematerials are contacted with an acidic solution and thereafter areprocessed in a conventional manner, they are not as catalytically activeas their higher aluminum- containing counterparts.

The novel process of this invention permits the preparation of certainhigh silica-containing materials which have all the desirable propertiesinherently possessed by such high silica materials and, yet, have anacid activity which heretofore has only been possible to be achieved bymaterials having a higher aluminum content in their "as synthesized"form. It further permits valuable activation of crystalline zeoliteshaving much lower silica-to-alumina mole ratios.

It is noted that U.S. Pat. Nos. 3,354,078 and 3,644,220 relate totreating crystalline aluminosilicates with volatile metal halides.Neither of these latter patents is, however, concerned with treatment ofcrystalline materials having a high silica-to-alumina mole ratio or withtreatment of any crystalline zeolite with ammoniacal aluminum flouridesin the present manner.

SUMMARY OF THE INVENTION

The present invention relates to a novel process for improving acidactivity of crystalline aluminosilicate zeolites, including highsilica-containing crystalline zeolites, which comprises the steps ofimpregnating the crystalline zeolite material with an ammoniacalaluminum fluoride solution, contacting the impregnated material with awarm aqueous solution of an ammonium salt (e.g. NH₄ NO₃) and calciningthe ammonium salt solution contacted material. The resulting zeolitematerial exhibits enhanced Bronsted acidity and, therefore, improvedacid activity toward catalysis of numerous chemical reactions, such as,for example, cracking of organic, e.g. hydrocarbon, compounds.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The novel process of this invention is concerned with the treatment ofcrystalline zeolites, including high silica-containing crystallinematerial. The expression "high silica-containing crystalline material"is intended to define a crystalline structure which has asilica-to-alumina ratio greater than 100 and more preferably greaterthan 500, up to and including those highly siliceous materials where thesilica-to-alumina ratio is infinity or as reasonably close to infinityas practically possible. This latter group of highly siliceous materialsis exemplified by U.S. Pat. Nos. 3,941,871; 4,061,724; 4,073,865 and4,104,294 wherein the materials are prepared from reaction solutionswhich involve no deliberate addition of aluminum. However, tracequantities of aluminum are usually present due to the impurity of thereaction solutions. It is to be understood that the expression "highsilica-containing crystalline material" also specifically includes thosematerials which have other metals besides silica and/or aluminaassociated therewith, such as boron, iron, chromium, etc. Thus, thestarting materials utilized in the novel process of this invention mayhave a silica-to-alumina ratio greater than about 100 (irrespective ofwhat other materials or metals are present in the crystal structure).

The zeolite starting materials utilized herein, including those having asilica-to-alumina mole ratio greater than about 100, may be preparedfrom reaction mixtures containing sources of various cations. Thepresent process provides noted improvement regardless of which cationsources are present in said reaction mixtures. Non-limiting examples ofcation sources to be used in the manufacture of the zeolite startingmaterials include amines, diamines, pyrrolidine, onium compounds andcompounds containing multiple cationic centers. Examples of oniumcompounds are those having the following formula:

    R.sub.4 M.sup.+ X.sup.-

wherein R is alkyl of from 1 to 20 carbon atoms, heteroalkyl of from 1to 20 carbon atoms, aryl, heteroaryl, cycloalkyl of from 3 to 6 carbonatoms, cycloheteroalkyl of from 3 to 6 carbon atoms, or combinationsthereof; M is a quadricoordinate element (e.g. nitrogen, phosphorus,arsenic, antimony or bismuth) or a heteroatom (e.g. N, O, S, Se, P, As,etc.) in an alicyclic, heteroalicyclic or heteroaromatic structure; andX is an anion (e.g. fluoride, chloride, bromide, iodide, hydroxide,acetate, sulfate, carboxylate, etc.). When M is a heteroatom in analicyclic, heteroalicyclic or heteroaromatic structure, such structuremay be, as non-limiting examples, ##STR1## wherein R' is alkyl of from 1to 20 carbon atoms, heteroalkyl of from 1 to 20 carbon atoms, aryl,heteroaryl, cycloalkyl of from 3 to 6 carbon atoms or cycloheteroalkylof from 3 to 6 carbon atoms.

The compounds containing multiple cationic centers include those havingthe formula:

    [(R).sub.3 M.sup.+ (Z).sub.n M.sup.+ (R).sub.3 ](X.sup.-).sub.2

wherein R, M and X are as above defined, Z is a bridging member selectedfrom the group consisting of alkyl of from 1 to 20 carbon atoms, alkenylof from 2 to 20 carbon atoms, aryl, heteroalkyl of from 1 to 20 carbonatoms, heteroalkenyl of from 2 to 20 carbon atoms and heteroaryl, and nis a number of from 1 to about 50. Non-limiting examples of suchmultiple cationic center containing compounds include: ##STR2##

The novel process of this invention is simple and easy to carry outalthough the results therefrom are dramatic. The process is carried outby impregnating the crystalline zeolite with an ammoniacal aluminumfluoride solution, said impregnation being conducted at a temperature offrom about 0° C. to about 100° C., preferably from about ambient toabout 50° C. The impregnated zeolite is then contacted with a warm, i.e.50° C. to 90° C., aqueous solution of from 0.1 to 2 Normal ammoniumsalt, e.g. 1N NH₄ NO₃, and thereafter calcined at a temperature of fromabout 200° C. to about 600° C. in an inert atomosphere of air, nitrogen,etc. at subatmospheric, atmospheric or superatmospheric pressures forfrom about 1 minute to about 48 hours.

The ammoniacal aluminum fluoride solution is composed of an aluminumfluoride, such as, for example, one selected from the group consistingof AlF₃, (NH₄)₃ AlF₆, (NH₄)₂ AlF₅ and NH₄ AlF₄, and concentratedammonium hydroxide or liquid ammonia. The amount of aluminum fluoride insaid solution will be from about 0.1 weight percent to about 5 weightpercent of the whole, with the amount of aluminum fluoride per gram ofcrystalline zeolite being treated during the impregnation step beingfrom about 0.1 to about 1 gram/gram.

The ammonium salt solution contacting step may be conducted for a periodof time of from about 1 hour to about 20 hours. The ammonium salt usedis not narrowly critical and will normally be an inorganic salt such asammonium nitrate, ammonium sulfate, ammonium chloride, etc.

Activation of zeolites with fluorides is generally believed to requirethe presence of an alumina material as a source of activation aluminum.In the present method, however, aluminum is provided by the aluminumfluoride component of the ammoniacal impregnating solution, with theammonia or ammonium hydroxide serving as an alumination vehicletransporting aluminum into the zeolite channels where new acid sites areformed. Therefore, supported or unsupported zeolites, including thosewhich have undergone severe thermal or hydrothermal deformation, may besuitably activated by the present method.

Of the high silica zeolite materials advantageously treated inaccordance herewith, zeolites ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35,ZSM-38 and ZSM-48 are particularly noted. ZSM-5 is described in U.S.Pat. No. 3,702,886 and U.S. Pat. No. Re 29,948, the entire contents ofeach being hereby incorporated by reference herein. ZSM-11 is describedin U.S. Pat. No. 3,709,979, the teaching of which is incorporated hereinby reference. ZSM-12 is described in U.S. Pat. No. 3,832,449, thecontents of which are incorporated herein by reference. ZSM-23 isdescribed in U.S. Pat. No. 4,076,842, the teaching of which isincorporated herein by reference. The contents of U.S. Pat. Nos.4,016,245 and 4,046,859, describing ZSM-35 and ZSM-38, respectively, areincorporated herein by reference.

ZSM-48 can be identified, in terms of moles of anhydrous oxides per 100moles of silica as follows: (0.05 to 5)N₂ O:(0.1 to 10)M_(2/n) O:(0 to4)Al₂ O₃ :(100)SiO₂ wherein M is at least one cation having a valence n,N is a mixture of a C₂ -C₁₂, and more preferably of a C₃ -C₅, alkylamineand a tetramethylammonium compound and wherein the composition ischaracterized by the distinctive X-ray diffraction pattern as shownbelow:

    ______________________________________                                        Characteristics Lines of Zeolite ZSM-48                                       d (A)        Relative Intensity (I/Io)                                        ______________________________________                                        11.8 ± 0.2                                                                              S                                                                10.2 ± 0.2                                                                              W-M                                                              7.2 ± 0.15                                                                              W                                                                4.2 ± 0.08                                                                              VS                                                               3.9 ± 0.08                                                                              VS                                                               3.6 ± 0.06                                                                              W                                                                3.1 ± 0.05                                                                              W                                                                2.85 ± 0.05                                                                             W                                                                ______________________________________                                    

These values were determined by standard techniques. The radiation wasthe K-alpha doublet of copper, and a diffractometer equipped with ascintillation counter and a strip chart pen recorder was used. The peakheights, I, and the positions as a function of two times theta, wheretheta is the Bragg angle, were read from the spectrometer chart. Fromthese, the relative intensities, 100 I/I_(o), where I_(o) is theintensity of the strongest line or peak, and d (obs.), the interplanarspacing in Angstroms (A) corresponding to the recorded lines, werecalculated. In the foregoing table the relative intensities are given interms of the symbols W=weak, VS=very strong, M=medium andW-M=weak-to-medium (depending on the cationic form). Ion exchange of thesodium ion with cations reveals substantially the same pattern with someminor shifts in interplanar spacing and variation in relative intensity.Other minor variations can occur depending on the silicon to aluminumratio of the particular sample, as well as if it has been subjected tothermal treatment.

ZSM-48 can be prepared from a reaction mixture containing a source ofsilica, tetramethylammonium compound, C₂ -C₁₂ alkylamine, an alkalimetal oxide, e.g. sodium, with or without a source of alumina, andwater, and having a composition, in terms of mole ratios of oxides,falling within the following ranges:

    ______________________________________                                        REACTANTS      BROAD       PREFERRED                                          ______________________________________                                        Al.sub.2 O.sub.3 /SiO.sub.2                                                                  0 to 0.08   0 to 0.02                                          Na.sub.2 O/SiO.sub.2                                                                         0.01 to 1.0 0.1 to 0.5                                         N.sub.2 O/SiO.sub.2                                                                          0.005 to 0.5                                                                              0.005 to 0.25                                      OH.sup.- /SiO.sub.2                                                                          0.01 to 0.5 0.05 to 0.2                                        H.sub.2 O/SiO.sub.2                                                                          10 to 200   20 to 100                                          ______________________________________                                    

wherein N is a mixture of a C₂ -C₁₂ alkylamine and tetramethylammoniumcompound, and maintaining the mixture at 80-200° C. until crystals ofZSM-48 are formed.

The molar ratio of C₂ -C₁₂ alkylamine to tetramethyl ammonium compoundis not narrowly critical and can range from 1:1 to 10:1. Thetetramethylammonium compound can include the hydroxide or halide withthe chloride being particularly preferred.

The original cations of ZSM-48 can be replaced, at least in part, bycalcination and/or ion exchange with another cation. Thus, the originalcations are exchanged into a hydrogen or hydrogen ion precursor form ora form in which the original cation has been replaced by a metal ofGroups II through VIII of the Periodic Table. Thus, for example, it iscontemplated that the original cations can be replaced with ammoniumions or with hydronium ions. Catalytically active forms of these wouldinclude, in particular, hydrogen, rare earth metals, aluminum, metals ofGroups II and VIII of the Periodic Table and manganese.

The activity enhanced materials prepared by the present process areuseful as catalyst components for acid catalyzed organic compoundconversion reactions. Such reactions include, as non-limiting examples,cracking of hydrocarbons, wherein the reaction conditions include atemperature of from about 300° C. to about 800° C., a pressure of fromabout 15 psia to about 500 psia, and a weight hourly space velocity offrom about 0.1 to about 20; and conversion of methanol to gasolinewherein the reaction conditions include a temperature of from about 300°C. to about 550° C., a pressure of from about 5 psia to about 500 psia,and a weight hourly space velocity of from about 0.1 to about 100.

In practicing a particularly desired chemical conversion process, it maybe useful to incorporate the above-described activity enhanced materialwith a matrix comprising a material resistant to the temperature andother conditions employed in the process. Such matrix material is usefulas a binder and imparts resistance to the catalyst for the severetemperature, pressure and reactant feed stream velocity conditionsencountered in many cracking processes.

Useful matrix materials include both synthetic and naturally occurringsubstances, as well as inorganic materials such as clay, silica and/ormetal oxides. The latter may be either naturally occurring or in theform of gelatinous precipitates or gels including mixtures of silica andmetal oxides. Naturally occurring clays which can be composited with thezeolite include those of the montmorillonite and kaolin families, whichfamilies include the sub-bentonites and the kaolins commonly known asDixie, McNamee, Georgia and Florida clays or others in which the mainmineral constituent is halloysite, kaolinite, dickite, nacrite oranauxite. Such clays can be used in the raw state as originally mined orinitially subjected to calcination, acid treatment or chemicalmodification.

In addition to the foregoing matrix materials, the catalyst employedherein may be composited with a porous matrix material such as alumina,silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, and silica-titania, as well as ternary compositions,such as silica-alumina-thoria, silica-alumina-zirconia,silica-alumina-magnesia and silica-magnesia-zirconia. The matrix may bein the form of a cogel. The relative proportions of activity enhancedzeolite component and matrix, on an anhydrous basis, may vary widelywith the activated zeolite content ranging from about 1 to about 99percent by weight and more usually in the range of about 5 to about 80percent by weight of the total dry composite.

The following examples will illustrate the novel method of the presentinvention.

EXAMPLE 1

Zeolite ZSM-5 was prepared from a reaction mixture containingtetraalkylammonium ions and having a silica-to-alumina mole ratio ofabout 26,000:1 (65 ppm framework alumina, 110 ppm bulk alumina and 0.23percent sodium). A sample of the ZSM-5 product of this example wascalcined for 30 minutes at 538° C.

EXAMPLE 2

An uncalcined portion of the zeolite prepared in Example 1 was vacuumimpregnated with saturated non-ammoniacal, aqueous aluminum fluoridesolution, i.e. (NH₄)₃ AlF₆ at 25° C. After 30 minutes impregnationcontact, the sample of zeolite was dried at 130° C. and contacted threetimes over an 18 hour period with 1N NH₄ NO₃ (26° C.). The sample wasthen washed, dried at 130° C. and calcined at 538° C.

EXAMPLE 3

An uncalcined portion of zeolite prepared in Example 1 was vacuumimpregnated at 25° C. with a saturated ammoniacal solution of (NH₄)₃AlF₆ (in concentrated NH₄ OH). It was then dried, treated with 1N NH₄NO₃ and calcined as in Example 2.

EXAMPLE 4

Another uncalcined portion of the zeolite prepared in Example 1 wasmixed with an equal weight of (NH₄)₃ AlF₆ and added to an equal volumeof solid ammonia. The ammonia was melted at about -70° C. and theresultant thin slurry was mixed throughly for 30 minutes at -70°to -30°C. The excess ammonia boiled off and the zeolite was heated with NH₄ NO₃(80° C.). The (NH₄)₃ AlF₆ was washed out by the process. The resultantzeolite was then calcined as in Example 3.

EXAMPLE 5

Another uncalcined portion of the zeolite prepared in Example 1 wastreated as in Example 3 except that a boron fluoride, i.e. NH₄ BF₄, wassubstituted for the aluminum fluoride, i.e. (NH₄)₃ AlF₆.

EXAMPLE 6

Zeolite ZSM-5 was prepared having a silica-to-alumina mole ratio of70:1. A sample of this zeolite was calcined in air for 60 minutes at1000° C.

EXAMPLE 7

A sample of the zeolite product of Example 6 was used for methanolconversion to hydrocarbons at 370° C., 0 psig and a WHSV of 1.4. After15 days on stream, the zeolite was regenerated by heating to 538° C. inair for 30 minutes. The regenerated zeolite was then impregnated with aboron fluoride, i.e. NH₄ BF₄, and treated with NH₄ NO₃ and calcined asin Example 5.

EXAMPLE 8

After measuring the Alpha Value of the product zeolite of Example 7 inthe Alpha Test, hereinafter described, it was then treated again as inExample 6 except that the impregnation was with an alkali metalfluoride, i.e. NaF, rather than the boron fluoride.

EXAMPLE 9

After measuring the Alpha Value of the product zeolite of Example 8, itwas then treated by the present method with an ammoniacal aluminumfluoride, ammonium salt solution and calcined as in Example 4.

EXAMPLE 10

Zeolite ZSM-5 was prepared having a silica-to-alumina mole ratio of250:1. The zeolite was activated by treatment with volatile AlCl₃ andcalcination for 30 minutes at 538° C. in air.

EXAMPLE 11

After measuring the Alpha Value of the activated zeolite product ofExample 10, it was then treated by the present method as in Example 3.

A sample of each final product of Example 1 through 11 was subjected tothe Alpha Test to measure catalytic activity. The results of these testsare listed below:

    ______________________________________                                        Example      Alpha Value                                                      ______________________________________                                        1            less than 0.1                                                    2            1.0                                                              3            30                                                               4            36                                                               5            0.7                                                              6            0.5                                                              7            2.2                                                              8            0.2                                                              9            8                                                                10           29                                                               11           60                                                               ______________________________________                                    

It is observed from the above results that the present method is highlyuseful for enhancing acid catalytic activity of crystalline zeolites,including those having a silica-to-alumina mole ratio greater than 100,which have, in turn, been impregnated with an ammoniacal aluminumfluoride solution, contacted with a warm aqueous solution of an ammoniumsalt, and calcined.

As is known in the art, the Alpha Value is an approximate indication ofthe catalytic cracking activity of the catalyst compared to a standardcatalyst and it gives the relative rate constant (rate of normal hexaneconversion per volume of catalyst per unit time). It is based on theactivity of the highly active silica-alumina cracking catalyst taken asan Alpha of 1. The Alpha Test is described in U.S. Pat. No. 3,354,078and in The Journal of Catalysis, Vol. IV, pp. 522-529 (August 1965).

What is claimed is:
 1. A method for enhancing the activity of a porouscrystalline zeolite having a silica-to-alumina mole ratio of 70 or morewhich comprises impregnating the zeolite at a temperature of from about0° C. to about 100° C. with an ammoniacal aluminum fluoride solutioncomprising from about 0.1 to about 5 weight percent of an aluminumfluoride in solution with at least one member selected from the groupconsisting of ammonium hydroxide and ammonia, contacting the impregnatedzeolite with a warm aqueous 0.1 to 2 Normal solution of an ammoniumsalt, and calcining the ammonium salt solution contacted material at atemperature of from about 200° C. to about 600° C.
 2. The method ofclaim 1 wherein said zeolite has a silica-to-alumina mole ratio greaterthan about
 100. 3. The method of claim 1 wherein said zeolite has asilica-to-alumina mole ratio greater than about
 500. 4. The method ofclaim 1 wherein said aluminum fluoride is at least one member selectedfrom the group consisting of AlF₃, (NH₄)₃ AlF₆, (NH₄)₂ AlF₅ and NH₄AlF₄.
 5. The method of claim 1 wherein said ammonium salt solution isammonium nitrate, ammonium sulfate or ammonium chloride.
 6. The methodof claim 1 wherein said zeolite is ZSM-5, ZSM-11, ZSM-12, ZSM-23,ZSM-35, ZSM-38 or ZSM-48.
 7. The method of claim 2 wherein said zeoliteis ZSM-5 or ZSM-11.
 8. A zeolite composition having enhanced activityprepared by the method of claim 1, 2, 3, 4, 5, 6 or 7.